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Bradford Protein Assay: Advantages & Disadvantages

Instructor: Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

There are several methods used to measure proteins. In this lesson we will examine the advantages and disadvantages of using the Bradford protein assay.

Bradford Protein Assay Overview

How much protein was in your dinner last night? How is the protein listed on nutrition facts labels determined? There are several different methods used, but one of the fastest ones is the Bradford protein assay.

The Bradford protein assay uses a blue dye that binds to specific amino acids, and the resulting intensity of blue color can be measured with a spectrophotometer. The resulting absorbance is compared to a standard to determine the concentration of protein in the sample.

Eggs are high in protein, the total of which can be measured using the Bradford protein assay
Eggs

This method is also called the Coomassie dye protein assay, due to the fact that the dye used is called a Coomassie dye. The name 'Bradford protein assay' comes from the first person to develop it, Marion M. Bradford. This method is fairly new, as it was developed within the last 50 years.

Advantages of the Bradford Protein Assay

The biggest advantage of the Bradford protein assay is its speed. The entire process only takes about a half hour. Once the test has been set up and the standard measured, each sample only takes a couple minutes to test. This allows several samples to be tested in a short amount of time, and retesting of a sample can be quickly performed.

The coomassie dye structure, which is used to identify proteins in a sample
Coomassie dye structure

Another advantage of this test is that is uses visible light (instead of UV light) to measure the absorbance of the sample. Many other samples use a wavelength of no higher than 280 nm, which is in the UV spectrum. Since this test uses 595 nm (which is in the visible light spectrum) laboratories do not need a UV spectrophotometer, and can rely simply on a visible light spectrophotometer.

The Bradford protein assay is also able to detect a large range of proteins, detecting amounts as small as 1 microgram in a sample.

Disadvantages of the Bradford Protein Assay

The biggest disadvantage of the Bradford protein assay is that it does not work if detergents or surfactants are in the sample or if the sample is basic. Particularly surfactants that are often used to solubilize some types of proteins will interfere with the test, causing the dye to precipitate out.

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